Need Power Supply: 120 VDC out at 3-6A

Discussion in 'The Projects Forum' started by technicom, Jan 30, 2011.

  1. technicom

    Thread Starter New Member

    Jun 29, 2010

    I need a 120 VDC power supply for a 120 VDC brushed motor. The brushed motor is rated for continuous duty. I have tried a simple full-wave bridge on the 120 VAC line, but the output is about 145 VDC. The motor gets too hot.

    I have used my Variac to reduce the AC line so that the full-wave bridge output is 120 VDC. The motor still gets warmer than I would like. If I add a filter capacitor to the circuit (250uF at 200 VDC) and turn the Variac down again so that the filtered output is 120 VDC, the motor runs much cooler...

    If I use an industrial power supply that outputs a "smooth" 120 VDC (i.e. virtually no ripple), the motor gets slightly warm, but does not get "too" warm.

    Why does the motor seem to get warmer with pulsating DC?

    Can anyone suggest a way for me to generate a relatively smooth 120 VDC from the 120 VAC line? The no-load current on the motor is about 700mA. The rated full-load current is 3 amps. The stall current is about 6 amps. The power supply must be able to generate 3 A continuously, but not be damaged if the motor stalls and momentarily (1-2 seconds) draws 6 A.

    Thanks in advance for your comments!

  2. beenthere

    Retired Moderator

    Apr 20, 2004
    If you can find a transformer with an 80 - 85 volt secondary voltage, that might work. The rectified DC will be pretty close to 120 VDC.

    Brushed motors are able to run on AC is they are series wound. Any idea about yours?